A friend asked me to find out car/motorbike stopping distances for her. Have speent last half hour with no luck been to Brake.org - tried Highway code- all to no avail.
any forum member know of chart/scale ?
I am Spartacus
some things are just too hard to find - when theyre under your nose.
"Remember such figures are not cast in stone"
Particularly in respect to the lorry stopping distances in the 3rd link.
A 6 axle artic will vary in weight from 14 tonnes unladen to 44 tonnes fully laden. This is a difference of 30 tonnes.
Beware when you cut in front of an obviously laden truck... we've all collected the trophies to prove the result:(
There is some interesting advice on the posted links. You can also use the equations of motion in a spreadsheet and work it out for yourself as this give some interesting results:
Stopping distance = u x t + (u^2) / 2 x f
u = speed from which you are stopping
t = thinking time and time to move your foot to the brake pedal
f = deceleration
30 MPH; 1 second thinking/moving time; 0.9 x g deceleration (g is the acceleration due to gravity (32 ft/s/s) and a modern car should achieve around 0.9 g on a good road; note I said car, other vehicles are different).
Change units to ft/s
30 MPH x 22/15 = 44ft/s (the factor 22/15 changes MPH to ft/s)
f = 0.9 x 32 = 28.8 ft/s/s
u x t = 44 x 1 = 44 ft
u^2 / 2 x f = 1936 / 57.6 = 33.6
So total stopping distance = 77.6 ft
Which is not too far away from the various quoted distances.
However, in a spreadsheet you can now try changing the numbers and be amazed!
Those who have remembered my going on about left foot braking in automatic cars change the 1 second thinking/moving time to 0.5 seconds (easy to achieve, it could be as low as 0.2 seconds but we won’t go too far). You will now see that a “left foot braker” can stop, from 37 MPH, in the same distance as a “normal” driver can from 30 MPH.
Now put in 70 MPH, 1 second thinking, 0.9 g and get 285 ft (a bit lower than published), but change to 0.1 g and see 1750 ft. Do you want to try to stop from 70 on ice?
If you are tired/ill/drunk or decide it is good fun to text on your mobile while driving, change the 1 second thinking time to 3 seconds.
And so on.
And then decide whether or not it is sensible to sit 6 inches behind the driver in front, even at low speeds...
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